#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0, i##_len=(n); i<i##_len; ++i)
#define pl(s) cout << s << endl;
using ll = long long;
constexpr long long MOD = 1000000007;
int main(void) {
  int ans = 0;
  int N; cin >> N;
  rep(i,N) ans += i+1;
  pl(ans)
  return 0;
}